The power required for the start-up of a tangential belt-driven working element having a whorl contacted by the belt is several times greater than the power required for maintaining the element at the operating speed (nominal speed) for accomplishing the purposes of the element which can, as noted, be a spindle in a spinning machine.
The degree to which the start-up power or acceleration-phase power exceeds the normal drive power depends essentially upon the mass of the working element to be accelerated, upon the time in which the element must be brought from standstill to the operating speed and, to a certain extent, upon the amount of work done by the element at its operating speed.
In start-up of an entire textile machine, e.g. a spinning frame, it is possible to protract the acceleration phase so that the starting power required for simultaneously bringing all of the spindles up to the nominal or operating speed is relatively small. Alternatively, it is possible to supply a start-up driving power which is augmented temporarily and which is reduced when the spindles of the machine are simultaneously brought up to speed.
This, however, requires for the application of the starting power an appropriately dimensioned belt-pressing force and/or an increased contact area between the belt and the whorls of the spindles of the entire machine. When the nominal rotary operating speed is achieved, the increased belt pressure and/or the increased contact area (i.e. the contact arc of the belt against the whorl) is no longer necessary.
To reduce the belt-processing work and the consequent energy losses, a centrally operated actuating mechanism is provided to simultaneously control the belt-pressing force for all of the working elements of the machine.
Such a central actuating mechanism is extremely expensive and complex, is prone to breakdown and requires considerable maintenance. It also is not helpful when it is necessary to accelerate individual working elements, for example, once a thread or yarn has been knotted after a thread breakage and the spindle is to be set in motion again. It makes little sense to reduce the speed of all unaffected working elements to allow one or a limited number to be brought up to nominal speed, for example, and even if this is done, the fluctuation in speed which would then result with operative spindles or working elements would result in the danger of yarn breakage or irregular winding of the bobbins or cops.
A similar problem is posed when a section of working elements of the machine are to be simultaneously accelerated to nominal or operating speed upon, for example, a partial change of bobbins or bobbin cores or sleeves.
When the remaining working elements are to be uninterrupted and not modified as to their speeds, in the latter case, the automatic actuating system operating upon all of the working elements cannot be used or, if used, creates problems including the possibility of altering the speed of the working elements which are to continue in operation.